1. Field of the Invention
This invention relates to a method for the production of an esterified product. More particularly, this invention relates to a method for the production of an esterified product of high quality, in the production of the esterified product by the esterification reaction of an alcohol with (meth)acrylic acid in a dehydrating solvent in the presence of an acid catalyst and a polymerization inhibitor.
Further, this invention relates to a method for the production of an alkoxy polyalkylene glycol mono(meth)acrylic acid type monomer for the use in a cement dispersant, and to a cement dispersant containing a polycarboxylic acid type copolymer using the monomer obtained by the method. More particularly, this invention relates to a method for the production of an alkoxy polyalkylene glycol mono(meth)acrylic acid type monomer which is capable of repressing the formation of impurities, particularly gel, liable to degrade the cement-dispersing ability by producing the alkoxy polyalkylene glycol mono(meth)acrylic acid type monomer by the esterification reaction of a polyalkylene glycol with (meth)acrylic acid in a dehydrating solvent in the presence of an acid catalyst and a polymerization inhibitor and which method is excellent in productivity (as evinced by a short reaction time and an outstanding reaction velocity), and to a cement dispersant containing a polycarboxylic acid type copolymer using a monomer obtained by the method mentioned above.
2. Description of the Related Art
Since the early deterioration of concrete structures became an object of social concern in 1981, the desirability of decreasing an unit water content in concrete and exalting durability and workability of concrete has been finding hearty approval. The development of a cement composition fulfilling this demand as well as the development of a cement dispersant which has a profound influence on the quality and performance of the cement composition has been promoted vigorously. The polymer component which is used in the cement dispersant, in pigment dispersants for calcium carbonate, carbon black, ink, and other pigments, and in scale removers, dispersants for a slurry of gypsum and water, dispersants for CWM, thickeners, and etc. is obtained by using a varying (meth)acrylic ester (occasionally referred to simply as "esterified product" in the present specification) to be obtained by the esterification of an alcohol with (meth)acrylic acid as a monomer component and polymerizing the monomer component.
It has been known that in this esterification, the alcohol and (meth)acrylic acid as the raw materials, the esterified product, or the mixture thereof are fated to be polymerized and form a gel. It is, therefore, usual to perform this esterification with a suitable polymerization inhibitor incorporated in the monomer mixture with a view to preventing this polymerization.
Among other inventions relating to the esterification reactions, JP-A-09-328,346 discloses a cement dispersant which contains a polymer (A) derived by using an alkoxy polyalkylene glycol (meth)acrylic ester type monomer obtained by subjecting an alkoxy polyalkylene glycol and a (meth)acrylic ester to the reaction of interesterification in the presence of a basic catalyst, a (meth)acrylic acid (salt) type monomer, and a monomer copolymerizable with such monomers and/or a polymer salt (B) obtained by further neutralizing the polymer (A) with an alkaline substance. Controls 1 and 2 cited in the patent publication mentioned above, as concrete examples of performing the esterification reaction in the presence of an acid catalyst, describe an operation of installing a reaction vessel provided with a reactor (a separable flask) incorporating therein a thermometer, a stirrer, and a water separating device and adapted to effect separation of the water formed by the reaction, charging the reaction vessel with methacrylic acid, methoxypolyethylene glycol (the average addition mol number of oxyethylene groups : 10 mols), sulfuric acid (Control 1) or paratoluene sulfonic acid (Control 2) as an acid catalyst, phenothiazine as a polymerization inhibitor, and cyclohexane as a dehydrating solvent, stirring and meanwhile heating the reactants therein to effect esterification and, at the same time, induce distillation of a cyclohexane-water azeotrope under normal pressure, removing water formed by the reaction with the water separating device and meanwhile refluxing cyclohexane.
The patent publication mentioned above, however, discloses that when the esterification is carried out in the presence of an acid catalyst, the acid catalyst is deficient in water-reducing properties as compared with a base catalyst and the esterification by the use of the acid catalyst by-produces (poly)alkylene glycol having hydroxyl groups at both terminals in consequence of ether cleavage of the alkoxy polyalkylene glycol, which by-product undergoes the esterification reaction with (meth)acrylic acid to give rise to a bifunctional di(meth)acrylic ester type monomer, and this monomer further acts as a cross-linking agent in the subsequent polymerization reaction and inevitably forms a cross-linked polymer having a high molecular weight and poor cement-dispersing properties. Specifically, in this patent publication, Table 1 showing the results of Controls 1 and 2 indicates that the relevant cross-linked components were formed in such large amounts respectively as of 12.0% and 14.6% during the reaction of the esterified products and that the esterification reactions both consumed long periods of 25 hours.
In addition to the drawback mentioned above, even the use of a proper polymerization inhibitor possibly results in forming a gel during the esterification as stated in the patent publication mentioned above. The occurrence of such gel proves extremely inconvenient in the case of mass production of a cement dispersant because of necessity of an extra process of separating the gel by filtration. To be specific, the operation of this production cannot be carried out continuously but must be stopped after each batch for the purpose of transferring the product into another device to separate by filtration the gel generated in the interior of the reaction vessel. Further, the part of the gel suffered to adhere to the inner wall of the reaction vessel is a mischievous entity liable to obstruct the continuous production because the inner wall must be washed to remove the gel and the work of this washing entails a needless addition to the number of production steps and requires to use a special device. As regards the fact that the gel occurs despite the use of an polymerization inhibitor, the patent publication mentioned above states that the esterification reaction, when carried out in the presence of an acid catalyst, by-produces (poly)alkylene glycol having hydroxyl groups at both terminals owing to ether cleavage of the alkoxy polyalkylene glycol as the raw material and suffers this by-product to undergo the esterification reaction with (meth)acrylic acid to give rise to a bifunctional di(meth)acrylic ester type monomer. No means of solving this problem, however, is disclosed anywhere in this patent publication. The esterification further has the problem that the polymer consequently obtained, when used in a proper application such as a cement dispersant, fails to manifest fully satisfactory cement-dispersing properties because the esterified product containing this di(meth)acrylic ester type monomer, on being polymerized, functions as a cross-linking agent and inevitably results in forming a cross-linked polymer having a high molecular weight and poor dispersing properties.
Regarding the method for esterifying in the presence of an acid catalyst, however, any means for repressing the formation of such impurities as mentioned above or any means for expediting the esterification reaction has never been reported to the literature.